The disclosure of Japanese Patent Application No.2001-054916 filed on Feb. 28, 2001, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
This invention generally relates to a driving control device and methods for a vehicle. More particularly, the present invention pertains to a driving control device and methods for independently controlling a steering angle, and a braking and driving force of each wheel.
2. Description of Related Art
A Japanese Patent Application Laid-Open No.11-500380 discloses a known driving control device which controls a yaw moment of a vehicle by independently controlling a braking force of each wheel depending on a vehicle model and a tire model. According to this driving control device, the vehicle will travel more stably compared to a vehicle in which the vehicle yaw moment is not controlled.
Generally, the vehicle motion is defined by a force generated in backward and forward direction (hereinafter referred as xe2x80x9clongitudinal forcexe2x80x9d), a lateral force, and a yaw moment of the vehicle. The longitudinal force, the lateral force, and the yaw moment of the vehicle are determined based on the direction and the strength of the force that each wheel generates relative to the road surface. In order to achieve a stable and appropriate vehicle travel that corresponds with the driving operation of the driver, the longitudinal force, the lateral force, and the yaw moment of the vehicle must be controlled based on respective target values that correspond to a steering operation, a driving force operation, and a braking force operation. Accordingly, the strength and the direction of the force generated by each wheel relative to the road surface must be controlled so that the longitudinal force, the lateral force, and the yaw moment of the vehicle are determined to be the respective target values.
Thus, according to the aforementioned known driving control device, because only braking and driving force are controlled based on the premise that the steering angle of a steering wheel corresponds to the steering operation of the driver and the steering angle of non-steering wheels is invariable, there is a limitation on the control range of the strength and the direction of the force that each wheel generates. Accordingly, the performance of the wheel (i.e., tire) cannot be demonstrated to the best of its potential, and thus, there is a need for improvements in the drivability of the foregoing known driving control device.
In conventional driving control devices, generally, the braking and driving force of respective wheels are independently controlled by a feedback control so that a deviation between a target behavior index of the vehicle, and an actual behavior index of the vehicle, is reduced. The vehicle motion control is performed based on how much the actual behavior of the vehicle has deviated from the target behavior. The feedback gain cannot be raised due to the necessity for ensuring the stability of the control such as prevention of a vehicle hunting. Thus, it has been difficult to effectively control the vehicle motion control.
Thus, the device and methods of the present invention consider the above-mentioned problems in the known driving control device which is constructed to control vehicle motion by controlling braking and driving force of independent wheel. The present invention improves the drivability compared to the known driving control device so that the vehicle motion can be securely and effectively controlled.
Accordingly, it is an object of the present invention to improve the drivability of a vehicle by expanding the control range of the strength and the direction of the force generated by each wheel by controlling steering angle of each wheel, and by controlling each wheel to meet the necessary strength and direction for achieving the appropriate vehicle motion that corresponds with the driving operation of the driver.
It is further object of the present invention to individually control a steering angle and a braking and driving force of each wheel by a steering angle controller and a braking and driving force controller.
In light of the foregoing, the present invention provides a driving control device and methods which include a first detector that detects a steering operation amount by a driver, a second detector that detects a driving force operation amount by the driver, and a third detector that detects a braking force operation amount by the driver. Moreover, a first calculator calculates a vehicle target longitudinal force, a vehicle target lateral force, and a vehicle target yaw moment based on the amounts detected by the detectors. A second calculator calculates a target generating force of each wheel based on the target longitudinal force, the target lateral force, and the target yaw moment, and a third calculator calculates a target steering angle and a target braking and driving force of each wheel based on the target generating force of each wheel. Finally, a first controller controls a steering angle and braking and driving torque of each wheel to be the target steering angle and the target braking and driving torque, respectively.
According to the present invention, the driving control device includes a second controller for independently controlling each wheel of the vehicle. The driving control device also calculates the vehicle target longitudinal force, the vehicle target lateral force, and the vehicle target yaw moment based on the amounts detected by the detectors. Moreover, it calculates the target generating force of each wheel based on the vehicle target longitudinal force, the vehicle target lateral force, and the vehicle target yaw moment, calculates the target steering angle and target braking and driving torque based on the target generating force of each wheel, and controls the steering angle and the braking and driving torque of each wheel to be determined as the target steering angle and the target steering and driving torque, respectively. Thus, the steering angle and the braking and driving torque of each wheel are controlled to correspond to the vehicle target longitudinal force, the vehicle target lateral force, and the vehicle target yaw moment by the generating force of each wheel. Accordingly, the vehicle drivability is significantly improved as compared to when only the braking and driving force of each wheel are controlled.